Lemmy, the idea is that you're not posting to your followers, but to a group, bypassing the notion of followers entirely. You ask a group to add a post to its collection of posts. IMO it's a powerful mechanism because it allows implementing all kinds of complex interactions without sacrificing your sanity. Walls, forums, group photo albums, all kinds of other things that people can contribute to. VK groups have a section with files for example, to which any group participant can upload new ones. You could do this with this mechanism, too.

Are you sure about a rewrite? It's mostly the same thing you already have except it's Add instead of Announce.